Airplane mode isn't the same as putting the phone inside a Faraday cage. The phone can tell the difference. Even in airplane mode the phone could receive rf; airplane mode is just supposed to disable transmission.

I think this is simply a matter of finding good defaults. In my opinion, the order of magnitude should be how many days without reception, not how many hours. A week sounds like a sane baseline for me, since that is more than ample time for most people to end up in a situation where you're connected again. Likewise you could reset the counter on a successful unlock. On the flip side, a week is not enough time to reasonably bruteforce anything if the time you have to wait before each retry goes up with every failure.

I dont think it is related to how long it has or not reception.

Also, it would be easy for cops to create a spoofed celular network to keep those phones with reception.

It look like it is based on how long since phone was last unlocked, i would say 1 week is even a big long in this case.. Just a couple of days should be more then enough.

It would need to be two weeks, one week is how long Burning Man lasts, and there is very little range there :)

I also spend a lot of time with my phone in airplane mode, but I'd have no problem with a reboot after two or three failed login attempts.

I'll be surprised if reading ebooks doesn't prevent an "inactivity reboot."

I'll be surprised if reading ebooks on a Kindle prevents an "inactivity reboot" on an iPhone...

That depends... Do you often go on flights longer than 96 hours?

Based on the article it almost sounds like multiple phones may have to be present